So I am having an interesting situation with this coin. I soaked it in acetone the other day, and due to unforeseen circumstances, I left it to soak for 36 hours. When I took it out, there was a real lightening of the copper around the edges, especially the reverse devices. I have allowed it to soak for 72 hours now, and I think it is gradually lightening more.
Is there anything destructive about this process for such an old coin? It seems like perhaps an old patina of grime, smoke, or another substance is very slowly dissolving.